1. Field of the Invention
This invention relates to solenoid actuators for switches and other electrical devices.
2. Description of Related Art
Although there have been many recent advances in the technology related to all-electronic switching devices, electromagnetic actuators are still required in many applications for which all-electronic devices are not suitable. As a result, there is a need for reliable electromagnetic actuators, particularly in applications where the device is subject to vibration, high impact, high acceleration, and fluctuating thermal and humidity conditions.
In the past, electromagnetic switching devices such as relays which were capable of withstanding these adverse conditions, have often been internally complex. As a result, many such prior devices are expensive and difficult to manufacture. For example, a typical prior relay is a model 412K Series T0-5 Relay manufactured by the Teledyne Corporation. This relay includes a clipper type armature having two small push pins with an insulating glass bead to push a contact reed from a first position to a second position when the electromagnetic force attracts the armature, and a larger return spring to push the armature to its first position when the electromagnet is deactivated. The construction of the armature as well as the complex arrangement of its contact members makes this relay difficult to manufacture. This design also has a relatively high number of moving parts and welded joints which are subject to failures. As a result, the reliability of this relay limits its usefulness in many applications.
Another previous design replaces the spring and armature system with a bar-shaped slider actuator which is mechanically coupled to the contact reed. The slider is provided with an off-axis permanent magnet which is normally attracted to the yoke and core of the electromagnet; thus, holding the slider and the contact reed in a first position. Activation of the electromagnet repels the permanent magnet moving the slider and the reed to a second position. Although an improvement over the aforementioned T0-5 relay, this design has a single stable position and consumes a substantial amount of power to repel the permanent magnet.
In still another design, an armature made of a ferro-magnetic material is positioned below an electromagnet. To increase resistance to shock and vibration, a permanent magnet is located such that the armature is held in one position by the attractive force of the permanent magnet. When the electromagnet of the actuator is activated, the attractive force of the electromagnet overcomes that of the permanent magnet, moving the armature to a second position. Such a design also consumes substantial power to overcome the permanent magnet.